Red light negatively affects health of stony coral

A new study led by Dr. Tim Wijgerde has concluded red light actively represses chlorophyll a and zooxanthellae growth in Stylophora pistillata whereas blue light appears to do the exact opposite.

A bank of red and blue LEDs over the experimental aquarium. Photo courtesy of Tim Wijgerde.

Using Philips LED lights, the researchers investigated how the SPS coral Stylophora pistillata would respond to light with varying intensity of blue and red light. Dr. Wijgerde, a regular Advanced Aquarist contributor, describes the finding of his research for us: "For zooxanthellae growth, blue and red are co-dominant, whereas for chlorophyll a synthesis, red light seems to be dominant over blue, inhibiting chlorophyll a production. This is logical, as within the first 10 meters red light is present. Thus, the coral seems to use red light to detect a high irradiance environment, reducing chlorophyll a, and thus photosynthetic efficiency, prevent light damage."

In layman's terms, the study reinforces the theory that corals use red light as their gauge for light intensity and regulates photosynthesis according to the amount of detected red light. With the popularity of red LEDs used in many modern lighting fixtures, reefkeepers should be conscientious of how much red light they use over their aquariums in light of this research. Note: red light is commonly found in proven lights such as Radium metal halides and numerous fluorescent bulbs as well as in wild reefs, so the idea is not that red light is necessarily harmful but that too much red light can have negative effects on how stony corals regulate photosynthesis.